1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to a disk drive identifying a starting track address by performing multiple load operations.
2. Description of the Prior Art
Disk drives comprise a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) in order to actuate the head radially over a disk. The VCM comprises a voice coil that generates a magnetic flux when energized with current. The magnetic flux generated by the voice coil interacts with magnetic flux generated by permanent magnets to generate a torque that rotates the actuator arm about the pivot. When the disk drive is powered down or idle, the head is parked in a landing zone at the inner diameter of the disk or unloaded onto a ramp at the outer diameter of the disk.
In disk drives employing ramp loading/unloading, an edge of the ramp typically extends out over a number of the servo tracks at the outer diameter of the disk. This allows a tab extending from the actuator arm to engage the ramp before the head “falls off” the outer diameter of the disk. It is desirable to determine how far the edge of the ramp extends over the outer diameter of the disk to maximize the usable recording surface of the disk. U.S. Pat. No. 5,559,648 discloses a method for detecting the edge of the ramp to identify the starting track (track 0) at the outer diameter of the disk prior to servo writing the disk using an external servo writer. The steps of detecting the edge of the ramp include moving the head to a known radial location, writing a known pattern (e.g., a clock pattern), and then attempting to read the known pattern. If the known pattern can be read without interference from the ramp, the head is moved radially outward and the process repeated until interference from the ramp prevents accurate detection of the known pattern. The starting track (track 0) is then identified as a marginal distance radially inward from the location where the interference is detected, and the external servo writer servo writes the disk from this starting track. Although this technique improves capacity (or reliability) by maximizing recording area across the disk surface, it increase the cost and complexity of the servo writing process. In addition, it precludes using an external media writer to servo write a disk which is subsequently installed into a disk drive.
There is, therefore, a need to identify a starting track in a disk drive at the outer diameter of a disk adjacent the edge of a ramp in order to optimize the recording density without significantly increasing the cost or complexity of servo writing the disk.